A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In both cases, the substrate and/or the mask must be moved across a projection beam that is generated by the apparatus. For this purpose a linear motor is typically provided, which drives a support structure (called a chuck) on which the substrate or mask is supported. The chuck is driven at high speeds in order to realize a high throughput. Existing chucks can be quite heavy, weighing e.g. as much as fifty kilograms. In order to reduce the load on the linear motor, the chuck is slideably supported on a support surface. Typically, the contact with the support surface is provided with air bearings and a suction cup, to minimize friction during motion and to prevent vertical movement of the chuck respectively.
The heavy weight of the chuck and its high speed of motion entail a substantial risk of damage when the chuck gets out of control. In particular, considerable collision forces may occur if the chuck would collide against the edge of the support surface at full speed. These forces can damage the linear motor and other parts of the lithographic apparatus.